Yiyan Wang

People inhabit a vast and intricate social network nowadays. In addition to our own decisions and actions, we confront those of various groups every day. Collective decisions and actions are more complex and bewildering compared to those made by individuals. As members of a collective, we contribute to its decisions, but our contributions may not always align with the outcome. We may also find ourselves excluded from certain groups and passively subjected to their influences without being aware of the source. We are used to being in overlapping groups and may switch identities, supporting or opposing the claims of particular groups. But rarely do we pause to think: What do we talk about when we talk about groups and their decisions? At the heart of this dissertation is the question of collective agency, i.e., in what sense can we treat a group as a rational agent capable of its action. There are two perspectives we take: a philosophical and logical one. The philosophical perspective mainly discusses the ontological and epistemological issues related to collective agency, sorts out the relevant philosophical history, and argues that the combination of a relational view of collective agency and a dispositional view of collective intentionality provides a rational and realistic account. The logical perspective is associated with formal theories of groups, it disregards the psychological content involved in the philosophical perspective, establishes a logical system that is sufficiently formal and objective, and axiomatizes the nature of a collective. The first topic that is addressed is the ontology of collective agency, i.e., the question what exactly is collective agency. The philosophical discussion of collective agency centres around the reduction problem of the concept of a collective. Individualism and Cartesian internalism have long influenced orthodox theories and made them face the choice between an irreducible concept of a collective and ontological reductionism. Heterodox theories such as functionalism and interpretationism reinterpret the concept of agency and accept it as also realized on the level of a collective. To adequately explain social phenomena that are essentially relational in nature, we propose a relational, holistic account of collective agency and argue that functionalism and interpretationism can be integrated into such an account. While acknowledging the irreducibility of the concept of a collective, we find that there is a deep incompatibility between the concept of a collective and the concept of intentionality as the mark of the mental. To explain how collective intentionality nevertheless is possible and why we tend to use it analogously to how we use the concept of individual intentionality, we explore a dispositional account of intentionality which enables us to give an account of the concept of intentionality at both the individual and collective level. Specifically, we subdivide the dispositional account into three aspects: behavioral, purely mental, and cognitive. We then argue that collective intentionality is real by analyzing different forms of attributive judgments of intentionality and by introducing the perspective of indispensable collective responsibility. We also analyze how philosophical theories about collective agency relate to central features of formal theories about collective decisions, such as game theory. Although the two fields are both concerned with collectives, there are also differences that need to be addressed. For example, game theory is clearly anti-psychologistic since its aim is a formal and objective analysis. However, from the relational and dispositional perspective, intentionality at the individual level and collective intentionality as we analyze it, inevitably involve mental content. In order to explain this difference and identify where the boundary is, we analyze the relationships between the three basic concepts involved, namely intentionality, preference, and dependency, so as to provide a unified picture of collective theory across philosophical and formal theories. After paving the nexus between philosophical and formal perspectives, the logical perspective becomes the theme of our discussion. To be able to express game theoretical concepts and to connect them to our philosophical perspective, We present a logic of preference and functional dependence and its hybrid extension, and provide an axiomatization which is sound and strongly complete. The decidability of this logic is also proved. Its application to modeling non-cooperative and cooperative games in strategic form is explored. The resulting framework provides a unified view of Nash equilibrium, Pareto optimality, and the core. The philosophical relevance of these game-theoretical notions to discussions of collective agency is made explicit. Finally, we conclude and clarify the position of our theory in the broader field of research on the topics addressed in the thesis. Also, we point out many new questions and directions suggested by our analysis, including philosophical and logical open problems.

This paper presents a logic of preference and functional dependence (LPFD) and its hybrid extension (HLPFD), both of whose sound and strongly complete axiomatization are provided. The decidability of LPFD is also proved. The application of LPFD and HLPFD to modelling cooperative games in strategic form is explored. The resulted framework provides a unified view on Nash equilibrium, Pareto optimality and the core. The philosophical relevance of these game-theoretical notions to discussions of collective agency is made explicit. Some key connections with other logics are also revealed, for example, the coalition logic, the logic of functional dependence and the logic of ceteris paribus preference.

Regarding collective agency, there have been two conflicting accounts, reducible and irreducible ones. This paper points out that the reason behind these two accounts and their irreconcilable status quo is that there is a tendency towards individualism and even naturalism with exisiting theories. This tendency comes with an unnecessary presupposition, which forces philosophers to face the tension between the irreducible group-concept and ontological monism. We propose a new perspective, that of a dispositional account, which can be considered as an alternative for the individualistic interpretation. We argue that it provides a better solution to the theoretical conundrums.

The discussion of collective agency involves the reduction problem of the concept of a collective. Individualism and Cartesian internalism have long restricted orthodox theories and made them face the tension between an irreducible concept of a collective and ontological reductionism. Heterodox theories as functionalism and interpretationism reinterpret the concept of agency and accept it as realized on the level of a collective. In order to adequately explain social phenomena that have relations as their essence, in this paper we propose a relational, holistic account of collective agency and argue that functionalism and interpretationism can be integrated into such an account.